Technical Field
The invention relates to technologies for producing nanostructured carbon material containing mainly carbon black combined with other carbon nanostructures such as nanotubes, nanofibers, fullerenes, onion-like structures, etc.
Description of the Related Art
Nanostructured carbon material is a mixture of micron and submicron carbon particles, such as carbon black, carbon nanotubes and nanofibers, fullerenes, onion-like structures, etc. In nanostructured carbon material based on carbon black, the latter predominates in terms of its content relative to other nanostructures contained in the material.
Here, the term “carbon nanostructures” is used to represent both carbon black particles and nanotubes, nanofibers, fullerenes, onions, and similar nanostructures.
Carbon black is widely used as a filler for polymers and rubbers that ensures improvement in their properties. However, an increase in the content of carbon black only yields a positive effect up to a certain limit.
The properties of polymers and rubbers can be considerably improved beyond this limit due to a small amount (approximately 1%) of elongated carbon nanostructures, such as nanofibers and nanotubes, included in the filler. Thus, introducing small amounts of carbon nanotubes into the polymer matrix improves such mechanical properties of a polymer as stiffness, impact elasticity, and strength. Application of carbon nanotubes mixed with carbon black or without it as the filler for tires affects the performance characteristics of a tire protector by increasing its wear resistance, rolling resistance, and tear strength.
High production cost and, as a result, high prices are the factors that prevent carbon nanotubes from being used as additives to the fillers of polymers and rubbers.
At the same time, there is a pressing need for an inexpensive and high-yield method for synthesis of large amounts of nanostructured carbon material that comprises elongated carbon nanostructures. For this reason, a challenge exists for creating a technology of producing nanostructured carbon material comprising nanotubes and/or nanofibers and other nanostructures.
The industrial production of carbon black, which is the most widely used nanostructured carbon material, is performed in special furnaces or chemical reactors by thermal decomposition of hydrocarbon feedstock in a turbulent stream.
There is a known method of producing carbon black by the thermal decomposition of natural gas or other methane-based hydrocarbon gases in regenerative gas heaters, see U.S. Pat. No. 3,445,190. The disadvantages of this method are low yield of carbon black, its contamination with mineral impurities, low electric conductivity of the produced carbon black and high consumption of energy resources for pyrolysis.
There is a known method of producing carbon black comprising the combustion of fuel with air, a supply of an axial flow of hydrocarbon feedstock and two coaxial flows of oxygen-containing gas, thermal decomposition of feedstock in the fuel combustion products to form gas-and-soot products, their thermal treatment at 1,450-1,550° C. for 0.2-0.5 s, subsequent cooling to 800-1,100° C. with water, and activation of the soot surface for 0.1-0.5 s, as well as quenching to 600-700° C. and separation of carbon black from gas products, see RU Patent No. 2116325. The disadvantage of this method is low quality of the produced carbon black, which necessitates its introduction as the filler of polymers and rubbers in high concentrations.
There is a known method of producing carbon black with good electrically conductive properties. The method comprises supplying a raw material mixture containing acetylene, hydrocarbons, and catalyst for carbon nanotubes formation into the high-temperature zone (with a temperature being equal or higher than the temperature of hydrocarbon thermal decomposition), and subsequent thermal treatment of the mixture, see U.S. Pat. No. 8,114,937. The produced material is composed by areas in the form of chains of spherical carbon particles connected with areas of rod-shaped carbon particles. The disadvantage of this method is the necessity of using expensive acetylene as the feedstock for producing carbon black, which increases considerably the expense of producing the product.
There is a known method of producing nanostructured carbon material based on carbon black by growing carbon nanotubes on the surface of prepared carbon black, see U.S. Publication No. 2008/0233402. This method is implemented by depositing a catalyst precursor onto the preliminarily produced carbon black, its subsequent conversion into a suitable catalyst for carbon nanotubes growth and heating in the presence of a carbon-containing gas up to 300-1,200° C. As this takes place, carbon nanotubes are grown on the surface of carbon black. The final stage is the cooling of the nanostructured carbon product produced by this method. This method of producing carbon material does not allow reproducing a carbon product with the same morphological composition including dimensions of carbon nanostructures, the ratio between the content of carbon black and carbon nanotubes, and, accordingly, with the same properties, such as electric conductivity, due to the fact that carbon nanotubes growth takes place on the surface of catalyst particles, which are formed on the surface of carbon black in the course of recovery of the catalyst precursor applied onto the surface of carbon black.